Method for making a metal-backed acetabular implant

ABSTRACT

A method of making a metal-backed acetabular implant includes roughening a surface of a metallic integument and compression molding a bearing to the surface after the roughening step.

FIELD OF THE INVENTION

The present invention relates generally to the field of orthopaedics,and, more particularly, to a method of making a metal-backed acetabularimplant for a hip prosthesis.

BACKGROUND

A conventional hip prosthesis is primarily composed of an acetabularimplant and a femoral implant. The acetabular implant typically includesa generally hemispherical dome-like or cup-like metallic shell securedwithin the acetabulum and a dome-like or cup-like plastic or ceramicbearing secured within the shell. Accordingly, the shell typicallyincludes an exterior configured to be anchored into the acetabulum andfurther typically includes an interior configured to align and retainthe bearing, while the bearing typically includes an exterior configuredto cooperate with the interior of the shell to align and secure thebearing within the shell and further typically includes an interiordefining an artificial hip socket (which may or may not be off-centeredfrom the exterior of the bearing, depending on the particular design).The femoral implant typically includes an elongated metallic spike orpost at one end and a metallic ball at the other. The post is typicallyconfigured to be anchored into the distal femoral medullary canal andthe ball is typically configured to insert into the artificial socket.Pivotal freedom of the ball within the socket allows articulation of theprosthetic joint.

A substantial dislocation and/or rotation of the bearing relative to theshell can potentially degrade the biomechanics and/or wearcharacteristics of the conventional hip prosthesis. Historically,balancing the needs for effective bearing retention with competingdesires for design simplicity and versatility has been challenging.

SUMMARY OF THE INVENTION

The present invention provides a method of making a metal-backedacetabular implant. The method includes roughening a surface of ametallic integument and compression molding a bearing to the surfaceafter the roughening step.

The above-noted features and advantages of the present invention, aswell as additional features and advantages, will be readily apparent tothose skilled in the art upon reference to the following detaileddescription and the accompanying drawings, which include a disclosure ofthe best mode of making and using the invention presently contemplated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary hip prosthesis including an exemplary femoralimplant and further including an exemplary acetabular implant accordingto the present invention;

FIG. 2 shows a perspective view of the exemplary acetabular implant ofFIG. 1;

FIG. 3 shows an exploded axial cross-sectional view of the exemplaryacetabular implant of FIG. 1;

FIG. 4 shows an axial cross-sectional view the shell of the exemplaryacetabular implant of FIG. 1;

FIG. 5 shows an axial cross-sectional view the bearing of the exemplaryacetabular implant of FIG. 1;

FIG. 6 shows an axial cross-sectional view of the integument of theexemplary acetabular implant of FIG. 1;

FIG. 7 shows an exploded axial cross-sectional view of an exemplaryalternative acetabular implant according to the present invention; and

FIG. 8 shows an exploded axial cross-sectional view of another exemplaryalternative acetabular implant according to the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

Like reference numerals refer to like parts throughout the followingdescription and the accompanying drawings. As used herein, the terms“medial,” “medially,” and the like mean pertaining to the middle, in ortoward the middle, and/or nearer to the middle of the body when standingupright. Conversely, the terms “lateral,” “laterally,” and the like areused herein as opposed to medial. For example, the medial side of theknee is the side closest to the other knee and the closest sides of theknees are medially facing, whereas the lateral side of the knee is theoutside of the knee and is laterally facing. Further, as used herein theterm “superior” means closer to the top of the head and/or farther fromthe bottom of the feet when standing upright. Conversely, the term“inferior” is used herein as opposed to superior. For example, the heartis superior to the stomach and the superior surface of the tongue restsagainst the palate, whereas the stomach is inferior to the heart and thepalate faces inferiorly toward the tongue. Also, as used herein theterms “anterior,” “anteriorly,” and the like mean nearer the front orfacing away from the front of the body when standing upright, as opposedto “posterior,” “posteriorly,” and the like, which mean nearer the backor facing away from the back of the body. Additionally, as used hereinthe term “generally hemispherical” is intended its broadest sense toencompass all concave and convex geometries suitable for applicablecomponents of prosthetic ball-and-socket type joints such as acetabularand glenoid shells, integuments, bearings, and the like, and,accordingly, includes hemispherical geometries, includes partiallyspherical geometries that are more than hemispherical, includespartially spherical geometries that are less than hemispherical, andincludes all suitable curved polygonal and geodesic geometries as well.Further, as used herein the terminology “taper couple” and inflectionsthereof mean to fasten together via a taper joint. In general, a taperjoint or taper coupling is formed by pressing together (“press-fitting”)a male part (“male taper”) and a female part (“female taper”) havingimpinging angled or flared surfaces. Taper couplings are generally knownin the art. For example, the disclosure of U.S. Pat. No. 6,610,097 toSerbousek et al, which is expressly incorporated herein by reference,discusses manners of making and using various taper couplings that maybe suitable for incorporation into applicable embodiments of the presentinvention.

FIG. 1 shows an exemplary hip prosthesis 100 including an exemplaryfemoral implant 120 and further including an exemplary acetabularimplant 140 according to the present invention. Among other things,implant 120 is configured as known to replace natural hip components(not shown) of a distal femur 160. In the exemplary embodiment, implant120 is metallic and preferably made from titanium. In alternativeembodiments, implant 120 may be made from a cobalt chrome alloy or anyother suitable biocompatible material(s). Implant 120 includes a post180. Among other things, post 180 is configured as known to anchor intoa medullary canal 200 of distal femur 160. Implant 120 also includes asubstantially spherical ball 220. Among other things, implant 140 isconfigured to replace natural hip components (not shown) of anacetabulum 240. Accordingly, implant 140 defines a generallyhemispherical artificial hip socket 260 (see FIG. 2 and FIG. 5) thatreceives ball 220 as known such that ball 220 has suitable pivotalfreedom within socket 260. Implant 140 is discussed further below.

FIG. 2 shows a perspective view of exemplary implant 140. Implant 140includes a dome-like or cup-like acetabular shell 300, and a dome-likeor cup-like metal-backed bearing sub-assembly 320 (see also FIG. 3).Among other things, shell 300 is configured to be anchored intoacetabulum 240 (see FIG. 1) in a known manner, and is configured totaper couple to sub-assembly 320 in accordance with the exemplaryembodiment. In the exemplary embodiment, shell 300 is metallic andpreferably made from titanium. In alternative embodiments, shell 300 maybe made from a cobalt chrome alloy or any other suitable biocompatiblematerial(s). Further, shell 300 is symmetrical about an axis 340 andincludes a generally concave inner surface 360 (see FIG. 4) defining agenerally concave cavity or socket 380 (see FIG. 4) that is symmetricalabout axis 340. Further, shell 300 includes a generally hemisphericalouter surface 400 facing generally outwardly away from socket 380. Inthe exemplary embodiment, surface 400 is suitably textured as known tofacilitate fixation in acetabulum 240. Additionally, it is noted thatsurface 400 may be suitably covered with a porous material (not shown)as known to enhance acetabular fixation of shell 300 through bone ingrowth.

FIG. 3 shows an exploded axial cross-sectional view of implant 140. Asat least partially discernable in FIG. 3, sub-assembly 320 includes adome-like or cup like bearing 406 and a dome-like or cup-like backing orintegument 412. Shell 300 and axis 340, among other things, are also atleast partially discernable in FIG. 3. Bearing 406 and integument 412are discussed further below.

FIG. 4 shows an axial cross-sectional view of shell 300. As at leastpartially discernable in FIG. 4, surface 360 of shell 300 includes anannular rim 420 centered about axis 340 with a radius 440. Surface 360also includes a circular flat 460 centered about axis 340 with a radius480. Flat 460 is disposed from rim 420 by an axial dimension 500. Socket380 opens at rim 420, while flat 460 bounds socket 380 axially inwardlyfrom rim 420. Further, surface 360 defines an annular female taper 520extending from flat 460 generally towards rim 420 at a taper angle 540relative to axis 340. Axially, taper 520 extends from flat 460 by adimension 560. Surface 360 also defines an annular female taper 580extending from taper 520 generally towards rim 420 at a taper angle 600relative to axis 340. Axially, taper 580 extends from taper 520 by adimension 620. Surface 360 also defines an annular female taper 640extending from taper 580 generally towards rim 420 at a taper angle 660relative to axis 340. Axially, taper 640 extends from taper 580 by adimension 680. In the exemplary embodiment, radius 480 is less thanradius 440, angle 600 is less than angle 540, and angle 660 is less thanangle 600, while dimension 620 is greater than dimension 560, anddimension 680 is greater than dimension 620.

FIG. 5 shows an axial cross-sectional view of bearing 406. Among otherthings, bearing 406 is configured as known to receive ball 220 (seeFIG. 1) in socket 260 and is configured to couple into integument 412according to the exemplary embodiment of the present invention. In theexemplary embodiment, bearing 406 is made from a plastic, preferablyultra high molecular weight polyethylene (“UHMWPE”). In alternativeembodiments, bearing 406 may be made from any other suitablebiocompatible material(s). As at least partially discernable in FIG. 5,bearing 406 includes a generally hemispherical and generally concaveinner surface 740 that is suitably machined as known to define socket260. Bearing 406 also includes a generally convex outer surface 760 thatfaces generally outwardly away from socket 260. Surface 760 includes anannular rim 820 centered about axis 340 with a radius 840. Surface 760also includes a circular flat 860 centered about axis 340 with a radius880. Flat 860 is disposed from rim 820 by an axial dimension 900.Further, surface 760 defines an annular male taper 920 extending fromflat 860 generally towards rim 820 at a taper angle 940 relative to axis340. Axially, taper 920 extends from flat 860 by a dimension 960.Surface 760 also defines an annular male taper 980 extending from taper920 generally towards rim 820 at a taper angle 1000 relative to axis340. Axially, taper 980 extends from taper 920 by a dimension 1020.Surface 760 also defines an annular male taper 1040 extending from taper980 generally towards rim 820 at a taper angle 1060 relative to axis340. Axially, taper 1040 extends from taper 980 by a dimension 1080. Inthe exemplary embodiment, radius 880 is less than radius 840, angle 1000is less than angle 940, and angle 1060 is less than angle 1000, whiledimension 1020 is greater than dimension 960, and dimension 1080 isgreater than dimension 1020.

FIG. 6 shows an axial cross-sectional view of integument 412. Amongother things, integument 412 is configured to couple around bearing 406and to couple into shell 300 according to the exemplary embodiment ofthe present invention. In the exemplary embodiment, integument 412 ismetallic and preferably made from titanium. In alternative embodiments,integument 412 may be made from a cobalt chrome alloy or any othersuitable biocompatible material(s). As at least partially discernable inFIG. 6, integument 412 includes a generally concave inner surface 1160that defines a generally concave socket 1170. Surface 1160 includes anannular rim 1220 centered about axis 340 with a radius 1240. Surface1160 also includes a circular flat 1260 centered about axis 340 with aradius 1280. Flat 1260 is disposed from rim 1220 by an axial dimension1300. Further, surface 1160 defines an annular female taper 1320extending from flat 1260 generally towards rim 1220 at a taper angle1340 relative to axis 340. Axially, taper 1320 extends from flat 1260 bya dimension 1360. Radius 1280, angle 1340 and dimension 1360 are sizedsuch that taper 1320 securely taper couples to taper 920 (of bearing406; see FIG. 5) upon assembly of sub-assembly 320 (see FIG. 3). Surface1160 also defines an annular female taper 1380 extending from taper 1320generally towards rim 1220 at a taper angle 1400 relative to axis 340.Axially, taper 1380 extends from taper 1320 by a dimension 1420. Angle1400 and dimension 1420 are sized such that taper 1380 securely tapercouples to taper 980 (of bearing 406; see FIG. 5) upon assembly ofsub-assembly 320 (see FIG. 3). Surface 1160 also defines an annularfemale taper 1440 extending from taper 1380 generally towards rim 1220at a taper angle 1460 relative to axis 340. Axially, taper 1440 extendsfrom taper 1380 by a dimension 1480. Angle 1460 and dimension 1480 aresized such that taper 1440 securely taper couples to taper 1040 (ofbearing 406; see FIG. 5) upon assembly of sub-assembly 320 (see FIG. 3).In the exemplary embodiment, dimension 1300 is about equal to dimension900 (of bearing 406; see FIG. 5), radius 1280 is less than radius 1240,angle 1400 is less than angle 1340, and angle 1460 is less than angle1400, while dimension 1420 is greater than dimension 1360, and dimension1480 is greater than dimension 1420.

Integument 412 also includes a generally convex outer surface 1560 thatfaces generally outwardly away from socket 1170. Surface 1560 includesan annular rim 1620 centered about axis 340 with a radius 1640. Surface1560 also includes a circular flat 1660 centered about axis 340 with aradius 1680. Flat 1660 is disposed from rim 1620 by an axial dimension1700. Further, surface 1560 defines an annular male taper 1720 extendingfrom flat 1660 generally towards rim 1620 at a taper angle 1740 relativeto axis 340. Axially, taper 1720 extends from flat 1660 by a dimension1760. Radius 1680, angle 1740 and dimension 1760 are sized such thattaper 1720 and flat 1660 have clearance with flat 460 and taper 520 uponassembly of implant 140. Surface 1560 also defines an annular male taper1780 extending from taper 1720 generally towards rim 1620 at a taperangle 1800 relative to axis 340. Axially, taper 1780 extends from taper1720 by a dimension 1820. Angle 1800 and dimension 1820 are sized suchthat taper 1780 has clearance with taper 580 upon assembly of implant140. Surface 1560 also defines an annular male taper 1840 extending fromtaper 1780 generally towards rim 1620 at a taper angle 1860 relative toaxis 340. Axially, taper 1840 extends from taper 1780 by a dimension1880. Angle 1860 and dimension 1880 are sized such that taper 1840securely taper couples to taper 640 (of shell 300; see FIG. 4) uponassembly of implant 140 (see FIG. 3). In the exemplary embodiment,dimension 1700 is less than dimension 500 (of shell 300; see FIG. 4),radius 1680 is less than radius 1640, angle 1800 is less than angle1740, and angle 1860 is less than angle 1800, while dimension 1820 isgreater than dimension 1760, and dimension 1880 is greater thandimension 1820.

To begin assembly of implant 140, bearing 406 is press-fitted axiallyinto socket 1170 (of integument 412) to assemble or unite sub-assembly320. Here, it is noted that although implant 140 is fully exploded inFIG. 3 for clarity of exposition, bearing 406 is preferablypre-operatively press-fitted into socket 1170 by a manufacturer to unitesub-assembly 320 separately from shell 300. Such pre-operativeunification of sub-assembly 320 may include temporarily cooling bearing406 (by immersing it in liquid nitrogen or by any other suitablerefrigeration method(s)) immediately prior to press-fitting it intosocket 1170, followed by allowing bearing 406 to warm or reheat to anormal temperature (and thus un-shrink or re-expand) within socket 1170so as to additionally tighten bearing 406 within socket 1170. Uponunification of sub-assembly 320, taper 1040 taper couples to taper 1440,which taper couples surface 760 to surface 1160, and, thus, tapercouples bearing 406 to integument 412. It is noted that the strength ofthe taper coupling reduces or eliminates needs for additionalundesirably complex and/or costly structures that might otherwise berequired to prevent dislocation and/or rotation of bearing 406 withinintegument 412.

Assembly of implant 140 is completed by suitably rotationally aligningsub-assembly 320 relative to shell 300 about axis 340 and thenpress-fitting sub-assembly 320 axially into socket 380 (of shell 300).Here, it is noted that the annular designs of taper 1720, taper 520,taper 1780, taper 580, taper 1840, and taper 640 allow for infiniterotational orientation or alignment of sub-assembly 320 (includingbearing 406 and, thus, socket 260 as well) prior to press-fittingsub-assembly 320 into socket 380. Such infinite rotational resolutionmay be especially advantageous for alternative embodiments of thepresent invention in which socket 260 is off-centered from axis 340.Upon press-fitting sub-assembly 320 into socket 380, taper 1840 tapercouples to taper 640, which taper couples surface 1560 to surface 360,and, thus, taper couples integument 412 (and thus, sub-assembly 320) toshell 300. It is noted that the strength of the taper coupling reducesor eliminates needs for additional undesirably complex and/or costlystructures that might otherwise be required to prevent dislocationand/or rotation of sub-assembly 320 within shell 300.

To assemble prosthesis 100, distal femur 160 and acetabulum 240 aresuitably resected, post 180 is suitably anchored into medullary canal200, and shell 300 is suitably anchored into acetabulum 240.Sub-assembly 320 is rotationally aligned relative to shell 300 and thenpress-fitted into socket 380. Lastly, ball 220 is inserted into socket260.

In operation of prosthesis 100, bearing 406 stays taper coupled tointegument 412 within socket 1170; sub-assembly 320 (including bearing406 and integument 412) stays taper coupled to shell 300 within socket380; and pivotal freedom of ball 220 within socket 260 allowsarticulation of implant 120 relative to implant 140.

FIG. 7 shows an exploded axial cross-sectional view of an exemplaryalternative acetabular implant 2000 according to the present invention.Implant 2000 is made and used in a like manner to implant 140 (discussedabove) except that sub-assembly 320 is replaced with an alternativedome-like or cup-like metal-backed bearing sub-assembly 2020.Sub-assembly 2020 includes an alternative dome-like or cup like bearing2100 and an alternative dome-like or cup-like backing or integument2120. Bearing 2100 is made and used in a like manner to bearing 406except that rim 820 is replaced with a radially inwardly extendingannular ledge 2200. Integument 2120 is made and used in a similar mannerto integument 412 except that rim 1220 is replaced with a radiallyinwardly extending annular flange 2300. When sub-assembly 2020 isunited, flange 2300 abuts ledge 2200 to additionally inhibit dislocationand/or rotation of bearing 2100 within integument 2120.

FIG. 8 shows an exploded axial cross-sectional view of another exemplaryalternative acetabular implant 3000 according to the present invention.Implant 3000 is made and used in a like manner to implant 140 (discussedabove) except that sub-assembly 320 is replaced with an alternativedome-like or cup-like metal-backed bearing sub-assembly 3020.Sub-assembly 3020 includes an alternative dome-like or cup like bearing3100 and an alternative dome-like or cup-like backing or integument3120. Bearing 3100 and integument 3120 are made and used in similarmanners to bearing 406 and integument 412, respectively, except thatbearing 3100 and integument 3120 are not taper coupled to each other;instead, surface 1160 is replaced with a generally hemisphericalgenerally concave surface 3160, and bearing 3100 is compression moldeddirectly onto surface 3160. Further, prior to compression moldingbearing 3100 onto surface 3160, surface 3160 is preferably roughened toproduce a more adherent substrate. The roughening is preferablyaccomplished by dry blasting surface 3160 with 60 grit alumina, or, inalternative embodiments, via any other suitable method.

The foregoing description of the invention is illustrative only, and isnot intended to limit the scope of the invention to the precise termsset forth. Further, although the invention has been described in detailwith reference to certain illustrative embodiments, variations andmodifications exist within the scope and spirit of the invention asdescribed and defined in the following claims.

1. A method of making a metal-backed acetabular implant, comprising thesteps of: roughening a surface of a metallic integument; and compressionmolding a bearing to the surface after the roughening step.
 2. Themethod of claim 1, wherein the bearing is substantially plastic.
 3. Themethod of claim 2, wherein the plastic is substantially ultra highmolecular weight polyethylene.
 4. The method of claim 1, wherein theroughening step includes dry blasting the surface.
 5. The method ofclaim 4, wherein the dry blasting step includes dry blasting the surfacewith a 60 grit material.
 6. The method of claim 5, wherein the 60 gritmaterial includes alumina.
 7. The method of claim 6, wherein the bearingis substantially plastic.
 8. The method of claim 7, wherein the plasticis substantially ultra high molecular weight polyethylene.
 9. The methodof claim 8, further comprising the step of taper coupling the integumentinto a metallic acetabular shell.